IMPROVED ROTARY ROLLER REAMER

Abstract: A rotary roller reamer (10) for a borehole has several rollers (11). Each roller (11) rotates about a fixed spindle (13) held at its ends in wedge blocks (14). The spindle (13) has two central passages (19), one at each end. At one end, passage (19) contains a freely slidable piston (21), which is subject to external pressure via a breather aperture (22). The other end passage (19) is blocked by a pressure plug (27) which, when removed, permits injection of grease through passages which include the bearing surfaces of the roller (11) and spindle (13). External pressure is applied to the grease through piston (21), so that there is little or no pressure differential to otherwise force mud into the bearing.

Description: "IMPROVED ROTARY ROLLER REAMER" This invention relates to a rotary roller reamer of the general type which is used in boreholes, and described and illustrated in the Applicant's earlier Australian Patent No 594885. The invention the subject of said earlier Patent overcame a number of problems which were encountered with prior art reamers, and one of the solutions to a problem previously encountered of failure of access to retaining screws was overcome by the use of end blocks retained by wedge blocks. That system has been shown to be very successful and is also embodied in this invention. In the aforesaid Patent bearing and spindle assemblies were contained at the ends of each roller, and within the blocks which were retained by the wedge blocks. Use was made of sealing rings to reduce the incidence of abrasive material lodging between the spindles and the bearing surfaces. However, pressure differential between the bearing surfaces at the outside of a drill string can become very considerable when the bore holes require reaming, due to very high pressures which can in some instances even extend to 3000 psi (20,000 kPa). If the reamer is adjacent the drill of a drill string (this being a usual requirement), it is required to operate near the bottom of a deep bore hole which is likely to contain grit or mud, and it has been found in practice that the grit and mud gets forced into the bearing between the spindle of a roller and bearing surface, and there have been instances where the bearings and their respective seals have been prematurely damaged. However, even if the reamer is located some distance above the bottom of the drill string, flushing water will carry grit and mud up past the reamer. The very high pressures encountered are usually due to flushing water. BRIEF SUMMARY OF THE INVENTION The main object of this invention is to provide a more satisfactory bearing arrangement, and this has been achieved by utilising a piston which floats freely in a cylindrical lubricant passage and lies between a bearing surface of the roller and the pressure space exterior of the roller, so that the piston will apply the same pressure to lubricant as the external pressure, thereby reducing the pressure differential and in turn retaining the lubricant in the bearing structure. Because of this improvement, and the success which has attended use of the end blocks and retaining wedges, it has been possible to revert to the earlier arrangement referred to as prior art in said Patent 594885 of the roller rotating around the stationary spindle. This in turn has provided means whereby the lubrication can be much improved and ingress of abrasive material can be much reduced. It also makes it feasible to have dual seals at each end of the bearing surfaces. Because of the improved sealing, invention may make use of ball or roller bearings to further assist in maintaining free rotation of the reamer. DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the invention is described hereunder in some further detail with reference to and is illustrated in the accompanying sketches in which: Fig 1 is a fragmentary view of a reamer body, showing two of three roller sets; Fig 2 is a longitudinal section through Fig 1 and drawn to a slightly larger scale; and Fig 3 is a split cross-section taken on line 3-3 of Fig 2, drawn to a still further larger scale. In this embodiment, a rotary roller reamer 10 is of the type which is used for reaming a hole cut by a drill on the end of a drill string. The functions of a reamer are first to maintain a hole size when wear causes the effective diameter of a drill to reduce, and second to smooth the surface of the borehole. The rotary roller reamer arrangement of this invention performs those functions. The reamer 10 shown in Fig 1 , contains several rollers 11 each with a plurality of tungsten carbide buttons 12 arranged circumferential ly around it. In the aforesaid Patent 594885, there was described and illustrated an arrangement wherein retaining wedges retained respective blocks in recesses extending axially along a reamer roller, and the blocks in that description contained bushes with O-rings at each end. The bearings were therefore external of the rollers, and assembly was effected at atmospheric pressure but when immersed into a deep bore hole containing water, there was a large pressure differential which was effective in forcing abrasive material past the O- rings and into contact with the bearing surfaces, and an object of this invention as said is to avoid that difficulty. Since the wedges and their blocks can be readily removed, in this embodiment the spindle 13 is retained in respect to the blocks 14 either by retainer fasteners, herein grub screws 15, and these come away with the blocks 14 when they are removed so that they can be separately removed and there is no access difficulty as with the early prior art. Running centrally part way into the spindle 13 from its ends are passages 19, shown partly in Fig 2 as being formed by the walls of an aperture extending from one end , and partly by the bore of a tube 20 extending from the other, the wall of tube 20 functioning as a heat transfer wall to reduce surface temperatures of the adjacent bearing. The tube 20 is illustrated to contain a piston 21 which can conveniently be of elastomeric material, and that piston is freely slidable within the tube 20. The outer end of the tube 20 opens to a "breather" aperture 22 in the reamer body, and the piston then being slidable imparts the same pressure inside the passage 19 as exists around the drill string, with very little pressure differential. This in turn makes it possible to utilise a much more satisfactory bearing arrangement than that achieved in the aforesaid Patent. The spindle 13 is retained as aforesaid, and the roller rotates over the spindle 13 with a large bearing area thereby reducing the bearing pressure on the rubbing surfaces. As the reamer is forced downwardly there is a great deal of thrust and this has previously been absorbed without the benefit of a fully designed thrust bearing, but in this embodiment some at least of the thrust is taken by an annular row of balls 24 contained between grooves 25 in the spindle and 26 in the interior wall of the roller 11. Those balls may be inserted before inserting the uppermost of the buttons 12, as shown in Fig 2. They therefore function as a deep groove ballbearing which will resist both radial and axial thrust in operation. The interior of the roller is charged with grease through a pressure plug 27, and that grease is pressured by the piston 21 to be the same as the external pressure. It is possible to use two resilient seals, and the resilient seals 28 between spindle 13 and roller 11 are lubricated by the grease and seal it against expulsion, while the resilient seals 29 sealing between a said block 14, spindle 13 and roller 11 , and performing the primary function of reducing the ingress of abrasive material to the seals 28 and the secondary function of partly effecting a seal against ingress of moisture. In order to ensure that the grease lies between the rubbing surfaces, the spindle 13 is provided with two flats 30 connected to the passages 19 through diametral apertures 31 , and this lubrication is of great importance in the difficult environment of a bore hole, flow of grease being impelled from tube 20 to the flats 30, and thereby to the bearing surface of spindle 13, by externally supplied pressure. For the above reasons, the invention the subject of this specification provides a valuable improvement over the aforesaid Australian Patent 594885 and over any other relevant prior art known to the Applicant.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. An improved rotary roller reamer of the type used in boreholes, and comprising a body having rollers contained in respective recesses defined by walls extending along a body of the reamer, the improvements comprising pairs of blocks, means retaining the blocks in the ends of said recesses, respective spindles carried by and extending between the blocks of each pair, walls defining a cylindrical passage extending in an axial direction in each said spindle, and further walls defining an aperture extending from said cylindrical passage to an outer surface of said spindle, a piston freely floatable in said passage between an outer end of said passage and said aperture, and a said roller rotatable on the outer surface of said spindle, so arranged that pressure imparted to an outer end of said piston is imparted by said piston to lubricant when contained in said passage and effective to impel flow of said lubricant through said aperture to said bearing surface. 2. An improved roller reamer according to claim 1 wherein said cylindrical passage opens to one end of said spindle, and at that said spindle end, walls define a breather space extending from said passage outer end to open to an environment which surrounds said reamer, said breather space being in communication with an outer end of said passage such that said pressure imparted to the outer end of said piston is the pressure of the environment which surrounds said reamer. 3. An improved roller reamer according to claim 2 comprising walls defining a further passage which is a second cylindrical passage extending in an axial direction from the other end of said spindle, and walls defining a second aperture extending from said second cylindrical passage to said outer surface of said spindle, each said aperture being diametral. 4. An improved roller reamer according to claim 3 wherein said second cylindrical passage terminates at said other end of said spindle in a pressure plug. 5. An improved roller reamer according to any preceding claim further comprising a tube contained within said spindle, the first said passage being defined by an inner surface of said tube. 6. An improved roller reamer according to claim 4 wherein said spindle outer surface is generally cylindrical, but has a flat portion to which each said diametral aperture opens. 7. An improved roller reamer according to any preceding claim further comprising two pairs of seals, one pair at each end of said spindle, the outer seal of each said pair sealing between a said block, spindle and roller and performing the function of reducing ingress of abrasive material, and the inner seal of each said pair sealing between said spindle and roller and sealing the lubricant against expulsion. 8. An improved roller reamer according to any preceding claim further comprising retainer fasteners co-acting between said blocks and said spindle to restrain rotation of said spindle.

Inventors: KENNEDY JOHN FRANCIS, KENNEDY, JOHN, FRANCIS
Applicants: GEARHART UNITED PTY LTD, KENNEDY JOHN FRANCIS, GEARHART UNITED PTY. LTD., KENNEDY, JOHN, FRANCIS
Application year: 1994
Main classification: E21B10
IPC codes: E21B10